The invention relates to a heat-triggered sprinkler used in fire fighting. More specifically, the invention relates to a sprinkler comprising a temperature-activated means, a housing, an inlet for a medium, a central nozzle, at least one side nozzle, a first channel for guiding the medium from the inlet to the central nozzle while the sprinkler is in its active state, and a second channel for guiding the medium from the inlet to said at least one side nozzle, the second channel being closed by means of a spindle means while the sprinkler is in a standby state, which spindle means, in the sprinkler's standby state, is in a housing channel of the housing in a first position, in which it is arranged to keep the second channel closed, and which spindle means, when the sprinkler is being activated due to the heat-activating means reacting to heat, is arranged to move to a second position and to open the second channel.
A sprinkler of the type described above is known from published international patent no. WO 95/31252. This known sprinkler is of a type, in which all its nozzles spray an extinguishing medium when the sprinkler transfers from its standby state, in which the temperature-activated means (ampoule) is intact, to its active state after the temperature-activated means breaks due to heat. After the temperature-activated means breaks, all the nozzles continue spraying as long as the extinguishing medium is fed into the inlet of the sprinkler.
The use of this known sprinkler in a fire extinguishing apparatus is normally problem-free. However, if this known sprinkler is used in applications, in which it is possible that hot combustible gases move far from the fire site because of airflows, the sprinklers transfer in the normal manner to said active state after the temperature-activated means has broken. The danger then exists that a great deal of the fire-extinguishing medium is sprayed on locations that do not need it. This unnecessarily sprayed extinguishing medium decreases the output of the spray nozzles close to the fire site, because the pressure of the extinguishing medium decreases below the design pressure of the fire extinguishing apparatus and/or the extinguisher fluid tank is emptied quicker than designed. Examples of such applications are tunnels, such as tunnels for vehicles. When sprinklers that are far from the fire site spray, the actual fire site does not receive the full output and there is a danger that the fire fighting fails or is inefficient with unfortunate results.